The present disclosure relates generally to switched mode power supplies, and especially to power supplies capable of generating and employing signals estimating an output current to a load.
A switched mode power supply commonly utilizes a power switch to control the current flowing through an inductive device. In comparison with other kinds of power supply, switched mode power supplies usually enjoy compact size and excellent conversion efficiency, and are accordingly popular in the art.
Power supplies with flyback topology are welcome because they provide Galvanic isolation. Flyback topology employs a transformer to direct-current isolate input power lines electrically connected to an AC mains outlet from output power lines electrically connected to a load. A primary side commonly refers to the side where the circuits are connected to input power lines, and a secondary side refers to the side where the circuits are connected to output power lines. Secondary side control uses resistors or devices in the secondary side to directly sense the current flowing to a load or the voltage across the load. Output voltage and current regulation can be easily achieved using secondary side control in expense of extra power consumption as the device in the secondary side constantly consume electrical power all the time, probably lowering power conversion efficiency. US patent application publication US20100321956A1, which is incorporated herein by reference in its entirety, discloses several switched mode power supplies employing primary side control to regulate their output currents in the secondary side. US patent application publication US20100321956A1 could make the maximum output current from a switched mode power supply a constant, independent from the voltages at input power lines.
Load compensation is a kind of skill to increase the output voltage of a power supply when an output current to a load increases, in order to compensate the voltage lost over the cables connected between a load and the power supply. One conventional method to achieve load compensation is by using a peak current through a transformer to represent the output current to a load and to adjust a target voltage that an output voltage of a power supply tends to approach. As known in the art, the peak current is so different from the output current and can hardly represent it.